The invention relates to a process and to a device for manufacturing seamed ends, especially tear open ends from hard-to-deform ferrous sheet metal in which the lacquer coated and with a rubber coated flange provided end, made of sheet metal bands of sheet metal plates is stamped and deformed.
End members of this kind are connected with their curled edge to a container (can body) by a double folded seam seal. To improve the sealing, rubber or elastomer bands are provided in the area of the edge of the end and are compressed between the container can body edge flange and the flange of the end in a double folded seam. Such ends are produced of sheet metal. Ferrous sheet metal is used in great amounts for this purpose which is provided in the form, for example, of tin coated sheet metal plates or sheet metal bands covered with a lacquer coat and with the annular rubber or elastomer coating according to a predetermined pattern and stamped then in the shape of ends and deformed. A score line or a prestamped opening may be provided at this time if easily to be opened cans are being produced.
On the surface of the end, the end flange is connected over a core bevel that is basically cylindrical and over an inner radius of a gage plate in the flange area proper and passes over a core wall curvature at the level of the end surface. The outer curled-on flange area is generally designated as end hook. The rubber coating is applied in the area of the end hook up to the inner radius of the gage ring.
Since the sheet metal is submitted during the formation of the end flange to an enormous deformation work, only respectively easily deformable expensive sheet metal could be applied heretofore for the fabrication of ferrous sheet metal ends. Less expensive sheet metal, for example, so called DR-sheet metal with an omitted last intermediate annealing were practically not used heretofore for the fabrication of ends of a thickness of less than 0.25 mm, since such hard-to-deform sheet metal that lies within the pricewise interesting range, tend to form flanged on the end hook. Such flange forming, however, leads to leakages within the double seam area. On the other hand, such sheet metal could offer special advantages in the process of fabrication of ends, not only in the area of cost savings. Such hard-to-deform sheet metal have thus better elasticity in preserve can ends, as well as higher nose forming strength, especially in ends for beverage cans.
It is the task of the invention to offer a process and a device with the help of which even the application of costs saving but hard-to-deform sheet metal can be used for the fabrication of ends, especially in the area of thicknesses that are costwise interesting without losing the advantage of lower costs of these sheet metals as to the cost of conventional sheets and without having to fear that the ends will leak within the sealing at the folded seam.
This task is solved according to the invention by that the curled-up and not by lacquer coated flange of the ends is re-annealed before its rubber coating had been applied for a period lasting less than 2 seconds in an atmosphere of inert gas. It can be prevented by this that the lacquer coating is applied to the sheet metal according to a predetermined pattern so that, during the lacquer coating, annular clearances of lacquer are produced which correspond to the flange areas of the stamped-out sheet metal, while these flange areas will be powder coated after the annealing. However, the preferred proceeding is that the blanks of sheet metal are stamped and the ends are submitted to an annealing of the flanges without being lacquer-coated, whereafter the end is submitted to a lacquer coating, preferably in the form of a powder coating before the application of a rubber coat in the flange area.
The annealing of the flange area is preferred as limited to the area of the end hook. According to the thickness of the sheet and its type, the annealing can reach also up to the core bevel. The core bevel itself and core wall curvature should, however, as far as possible, be excepted. This goes also for the gage ring's inner radius. The re-annealing, especially, should reach only as far as the increased nose-forming strength of the applied sheet metal is exploited to its full extent in comparison with that of conventional sheet metal.
The new process can be applied for sheet metal ends of different nominal diameters, especially within a range of nominal diameters from 57 to 63 mm. The initial hardness of the sheet metal, related to the known designations of sheet metals can be greater or equal to hardnesses of sheet metals of the specification DR 8, DR 9 and DR 10, while the thicknesses are foreseen within the range between 0.1 mm and 0.3 mm, preferably within the range equal or less than 0.25 to 0.15 mm. The diameter, the hardness of the sheet metal and its thickness depend among others also on the application of the can that is provided with the end. Especially suitable is the end for sealing usual preserve cans, coffee cans, beer cans or other beverage cans, cans for mineral oil, etc.
The results of examinations was that the thus processed sheet metal ends can be sealed without forming folds and without any danger of leakages done perfectly on conventional machines with double seam sealing with the respective cans or containers.
Preferably slightly tin-coated fine sheets are used and the annealing temperatures of the period of annealing are selected so that the tin coat is fused within a short period of time, however, without evaportion or damaging of any kind and brought again to a hardening. According to the annealing in a ring inductor, according to the thickness of the material and the width of annealing, the time of annealing can vary. It should last for less than 0.1 sec, since otherwise a damage or destruction of the materials to be annealed is to be feared by occuring whirling streams. The times of annealing should preferably amount to an annealing width of 2 or 3 mm of the outermost end flange within the range from 0.02 to 0.06 seconds, related to the annealing of 1200 ends/min with a ring inductor of 20 kw (300 kHz). Should the entire end flange (of the gage ring radius exclusively) or of metal sheets of a greater thickness be annealed, a higher amount of energy, resp. a longer time of annealing is necessary.